World population continues to increase at a frightening rate, particularly rate, particularly in developing countries. At the 1990 fertility rate (approximately 4 children per woman world-wide) there would be over 75 billion people on earth in year 2100, compared to 6 billion at the present time. Even at the very optimistic projection of 2.5 children per woman, global population will grow to 19 billion by the year 2100. A recent Joint Statement of the fifty-eight of the World's Scientific Academies (including the National Academy of Sciences of the U.S.A.) concluded: "Humanity is approaching a crisis point with respect to the interlocking issues of population, environment and development. Scientists today have the opportunity and responsibility to mount a concerted effort to confront our human predicament...The academics believe that ultimate success in dealing with global social, economic and environmental problems cannot be achieved without a stable world population...Family planning could bring more benefits to more people at less cost than any other single technology now available to the human race." The work proposed in this application is designed to increase our basic and clinical knowledge of reproductive processes in the male. We are committed to excellence across the spectrum of studies proposed, from basic molecular biology and biochemistry through human physiology with direct application to contraceptive development and the treatment of infertility. Our proposed incorporate the talents of outstanding reproductive biology. We have structured this Center to meld superb science with the practical goal of applying new basic knowledge as quickly as possible to studies in human beings. We hope that, in this way, our work will address critical needs of society such as the dramatic growth of world population.